Matt Murdock needs not see the child waving him down to know he's being spoken to, though perhaps Atreus might not realize that at first, with his eyes hidden behind wine-dark glasses. He pauses nonetheless, his face not quite pointed completely in the youngster's direction, but unmistakably paying attention. "I know a few. Are you collecting them?"

That sounds like the ruffling of empty pages, and he can smell the pungent aroma of fresh tooled leather and the milder scent of ink. What's on the pages, of course, he can't really guess, but context clues seem to lean that way.